1. Field of the Invention
The present invention relates to an image processing apparatus and to an image processing method for computer graphics.
2. Related Arts
In image processing using computer graphics, normally, a polygon model is generated in three-dimensional coordinate space, and hidden surface removal and shading processes are performed for the polygon model. The obtained model is converted into a model with two-dimensional coordinates, which is then superimposed on a background screen. In this case, in order to highlight the model on the background screen, a special calculation is performed for the model data to simplify the gray scaling of the model or to add an outline to the model.
For example, for software used for preparing a 3D-CG image, a polygon model in three-dimensional coordinate space is projected onto a two-dimensional screen, the boundary between the projected model and the background screen is calculated, and a line having a designated width is drawn along the boundary to generate the outline.
As is described above, in conventional three-dimensional computer graphics, the process of generating the outline for a model is performed by extracting portions of three-dimensional polygon models for which an outline should be generated, and by drawing a line having a designated width at the extracted portions. Thus, the load is increased which is placed on the calculations performed to identify the portions of the polygon models where the outline is to be generated, and an extended time is required for the process of generating the outline.
However, in a game machine, for example, which employs computer graphics, models must be changed in real time in accordance with instructions entered by a player. And since according to the conventional outline generation method an outline is generated by calculating the boundary between changing models, an extended time is needed for the required calculations. Thus, in a game machine for which it is important that a model respond immediately to manipulation by a player, the process of generating an outline for a model can not be performed in real time.
In addition, since according to the conventional method the outline is generated by drawing a line having a designated width along the boundary between a model and a background screen, regardless of the distance between the model and a camera, a perspective view of the model can not be obtained by changing the line width of the outline.